U.S. patent application number 15/161674 was filed with the patent office on 2016-12-01 for method of forming metal film.
The applicant listed for this patent is TOKYO ELECTRON LIMITED. Invention is credited to Yasushi AIBA, Takanobu HOTTA, Koji MAEKAWA, Kenji SUZUKI.
Application Number | 20160348234 15/161674 |
Document ID | / |
Family ID | 57398126 |
Filed Date | 2016-12-01 |
United States Patent
Application |
20160348234 |
Kind Code |
A1 |
SUZUKI; Kenji ; et
al. |
December 1, 2016 |
Method of Forming Metal Film
Abstract
There is provided a method for forming a metal film on a target
substrate having a complex-shaped portion and a flat portion, the
target substrate being loaded into a chamber which is maintained
under a depressurized atmosphere, by sequentially supplying a metal
chloride gas as a raw material gas and a reduction gas for reducing
a metal chloride into the chamber while purging the chamber in the
course of sequentially supplying the metal chloride gas and the
reduction gas, the method including: forming a first metal film by
supplying the metal chloride gas at a relatively low flow rate; and
forming a second metal film by supply the metal chloride gas at a
relatively high flow rate.
Inventors: |
SUZUKI; Kenji; (Tokyo,
JP) ; HOTTA; Takanobu; (Nirasaki City, JP) ;
MAEKAWA; Koji; (Nirasaki City, JP) ; AIBA;
Yasushi; (Nirasaki City, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOKYO ELECTRON LIMITED |
Tokyo |
|
JP |
|
|
Family ID: |
57398126 |
Appl. No.: |
15/161674 |
Filed: |
May 23, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 16/45527 20130101;
H01L 21/28562 20130101; H01L 21/76877 20130101; H01L 27/11582
20130101; C23C 16/14 20130101; C23C 16/045 20130101 |
International
Class: |
C23C 16/06 20060101
C23C016/06; C23C 16/455 20060101 C23C016/455 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2015 |
JP |
2015-108445 |
Claims
1. A method for forming a metal film on a target substrate having a
complex-shaped portion and a flat portion, the target substrate
being loaded into a chamber which is maintained under a
depressurized atmosphere, by sequentially supplying a metal
chloride gas as a raw material gas and a reduction gas for reducing
a metal chloride into the chamber while purging the chamber in the
course of sequentially supplying the metal chloride gas and the
reduction gas, the method comprising: forming a first metal film by
supplying the metal chloride gas at a relatively low flow rate; and
forming a second metal film by supply the metal chloride gas at a
relatively high flow rate.
2. The method of claim 1, wherein the forming a first metal film
and the forming a second metal film are alternately performed.
3. The method of claim 1, wherein the target substrate has a base
film formed thereon, and the first metal film is formed on the base
film.
4. The method of claim 1, wherein the target substrate has a base
film formed thereon, and an initial metal film is formed between
the metal film and the base film by sequentially supplying the
metal chloride gas and the reduction gas into the chamber while
supplying a purge gas in the course of sequentially supplying the
metal chloride gas and the reduction gas, or by simultaneously
supplying the metal chloride gas and the reduction gas into the
chamber, wherein a flow rate of the metal chloride gas is lower
than that used in forming the second metal film.
5. The method of claim 1, wherein a final stage in the formation of
the metal film is the forming a first metal film.
6. The method of claim 1, wherein a top coating metal film is
formed on the metal film by sequentially supplying the metal
chloride gas and the reduction gas into the chamber while supplying
a purge gas in the course of sequentially supplying the metal
chloride gas and the reduction gas, or by simultaneously supplying
the metal chloride gas and the reduction gas into the chamber,
wherein a flow rate of the metal chloride gas is lower than that
used in forming the second metal film.
7. The method of claim 1, wherein a tungsten chloride is used as
the metal chloride to form a tungsten film as the metal film.
8. The method of claim 7, wherein gas of the tungsten chloride is
supplied such that a partial pressure of the tungsten chloride gas
inside the chamber in the forming the first metal film is 1 Torr or
less.
9. The method of claim 7, wherein gas of the tungsten chloride is
supplied such that a partial pressure of the tungsten chloride gas
inside the chamber in the forming the second metal film falls
within a range from 0.5 to 10 Torr.
10. The method of claim 7, wherein, in the forming the first metal
film and the second metal film, a temperature of the target
substrate is 300 degrees C. or more, and an internal pressure of
the chamber is 5 Torr or more.
11. The method of claim 7, wherein the tungsten chloride includes
one of WCl.sub.6, WCl.sub.5, and WCl.sub.4.
12. The method of claim 1, wherein the reduction gas is at least
one of an H.sub.2 gas, an SiH.sub.4 gas, a B.sub.2H.sub.6 gas and
an NH.sub.3 gas.
13. A non-transitory computer-readable storage medium storing a
program that operates on a computer and controls a film forming
apparatus, wherein the program, when executed, causes the computer
to control the film forming apparatus so as to perform the method
of claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of Japanese Patent
Application No. 2015-108445, filed on May 28, 2015, in the Japan
Patent Office, the disclosure of which is incorporated herein in
its entirety by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a method for forming a
metal film.
BACKGROUND
[0003] In manufacturing a large-scale integration (LSI), tungsten
has been widely used for MOSFET gate electrodes, source-drain
contacts, memory wordlines and the like. A Cu wiring has been
mainly used in a multilayer wiring process. However, Cu has a poor
heat resistance and is easily diffused. As such, tungsten has been
used for a portion that requires a heat resistance or a portion of
which an electric property may deteriorate due to the diffusion of
Cu.
[0004] A physical vapor deposition (PVD) method has been used as a
film forming process of a tungsten film. However, it is difficult
to use such a PVD method for a portion that requires a high
coverage rate (step coverage). Because of this, a chemical vapor
deposition (CVD) method which provides good step coverage has been
performed to form the tungsten film.
[0005] As a method of forming a tungsten film (CVD-tungsten film)
using such a CVD method, a method of inducing a reaction of
WF.sub.6+3H.sub.2.fwdarw.W+6HF on a semiconductor wafer as a target
substrate, by using a tungsten hexafluoride (WF.sub.6) as a raw
material gas and an H.sub.2 gas as a reduction gas, is generally
used.
[0006] However, when the tungsten film is formed by the CVD method
using the WF.sub.6 gas, fluorine contained in WF.sub.6 reduces a
gate insulation film in a semiconductor device, particularly in
gate electrodes, memory wordlines or the like, which deteriorates
an electric property of the semiconductor device.
[0007] As a raw material gas used in forming a CVD-tungsten film
containing no fluorine, tungsten hexachloride (WCl.sub.6) is known.
Although chlorine has a reduction property like fluorine,
reactivity of chlorine is weaker than that of fluorine. As such,
chlorine is expected to hardly affect the electric property.
[0008] In recent years, as the semiconductor device becomes finer
and finer, it is difficult to use the CVD method, which is known to
provide good step coverage, to bury a film into a complex-shaped
pattern. Thus, from the viewpoint of obtaining higher step
coverage, an atomic layer deposition (ALD) method which
sequentially supplies a raw material gas and a reduction gas while
performing a purge process in the course of sequentially supplying
the raw material gas and the reduction gas, is getting a lot of
attention.
[0009] In some instances, a complex-shaped semiconductor device
such as a three-dimensional (3D) NAND flash memory has been
developed. Formation of a tungsten film on such a complex-shaped
semiconductor device requires supplying a film-forming raw material
at a high flow rate.
[0010] Meanwhile, there are generally simple flat portions such as
peripheral circuits even in the complex-shaped semiconductor
device. In forming a film on the device having such complex-shaped
and flat portions by using a chloride such as tungsten hexachloride
(WCl.sub.6) as a film-forming raw material, if the chloride raw
material is supplied at a flow rate that is required to form the
film on the complex-shaped portion, hardly any of the film will be
formed on the flat portion.
SUMMARY
[0011] Some embodiments of the present disclosure provide to a
method for forming a metal film on a target substrate having
complex-shaped and flat portions using a chloride raw material such
that the metal film is formed both in the complex-shaped and flat
portions.
[0012] According to one embodiment of the present disclosure, there
is provided a method for forming a metal film on a target substrate
having a complex-shaped portion and a flat portion, the target
substrate being loaded into a chamber which is maintained under a
depressurized atmosphere, by sequentially supplying a metal
chloride gas as a raw material gas and a reduction gas for reducing
a metal chloride into the chamber while purging the chamber in the
course of sequentially supplying the metal chloride gas and the
reduction gas, the method including: forming a first metal film by
supplying the metal chloride gas at a relatively low flow rate; and
forming a second metal film by supply the metal chloride gas at a
relatively high flow rate.
[0013] According to another embodiment of the present disclosure,
there is provided a non-transitory computer-readable storage medium
storing a program that operates on a computer and controls a film
forming apparatus, wherein the program, when executed, causes the
computer to control the film forming apparatus so as to perform the
aforementioned method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the present disclosure, and together with the general description
given above and the detailed description of the embodiments given
below, serve to explain the principles of the present
disclosure.
[0015] FIG. 1 is a sectional view showing an example of a tungsten
film forming apparatus which is used in implementing a metal film
forming method according to the present disclosure.
[0016] FIGS. 2A and 2B are cross-sectional process views
schematically showing processes of a tungsten film forming method
which is one embodiment of the metal film forming method according
to the present disclosure.
[0017] FIG. 3 is a view schematically showing a film formation
state when a tungsten film is formed using a WCl.sub.6 gas and an
H.sub.2 gas by an ALD method.
[0018] FIGS. 4A and 4B are views schematically showing film
formation states when the tungsten film is formed on a flat portion
and a patterned portion using the WCl.sub.6 gas and the H.sub.2 gas
by the ALD method.
[0019] FIGS. 5A to 5C are cross-sectional process views explaining
a process of manufacturing a 3D NAND flash memory.
[0020] FIGS. 6A and 6B are cross-sectional process views explaining
a process of manufacturing the 3D NAND flash memory.
[0021] FIG. 7 is a view showing a relationship between a cycle rate
(deposition amount per cycle) and a step coverage in the ALD
method, when the tungsten film is formed on a flat portion and a
complex-shaped portion using the WCl.sub.6 gas and the H.sub.2 gas
by the ALD method.
[0022] FIG. 8 is a cross-sectional view schematically showing a
state where an initial tungsten film is formed between a base film
and a tungsten film.
[0023] FIGS. 9A to 9C are views illustrating a problem that is
caused when the tungsten film is subjected to a wet etching.
[0024] FIG. 10 is a cross-sectional view schematically showing a
state where a top coating tungsten film is formed on the tungsten
film.
[0025] FIG. 11 is a view showing an example of a gas supply
sequence by which a first tungsten film and a second tungsten film
are formed.
[0026] FIG. 12 is a view showing another example of the gas supply
sequence by which the first tungsten film and the second tungsten
film are formed.
DETAILED DESCRIPTION
[0027] Reference will now be made in detail to various embodiments,
examples of which are illustrated in the accompanying drawings. In
the following detailed description, numerous specific details are
set forth in order to provide a thorough understanding of the
present disclosure. However, it will be apparent to one of ordinary
skill in the art that the present disclosure may be practiced
without these specific details. In other instances, well-known
methods, procedures, systems, and components have not been
described in detail so as not to unnecessarily obscure aspects of
the various embodiments.
[0028] The present inventors have studied a reason why, if a metal
chloride is supplied at a flow rate that is required to form a film
on a complex-shaped portion, hardly any of the film is formed on a
flat portion. As a result, the present inventors found that when
the film is formed using the metal chloride such as tungsten
hexachloride (WCl.sub.6), HCl is created as a by-product which
induces an etching action on the formed film, and an amount of HCl
per unit area is relatively large in the flat portion so that such
an etching action is significantly exerted in the flat portion. As
a result of the earnest study, the present inventors found that if
the metal chloride raw material is supplied at a relatively low
flow rate, the film can be formed on the flat portion, whereas if
the metal chloride raw material is supplied at a relatively high
flow rate, the film can be formed on the entire region of the
complex-shaped portion. Thus, the present inventors completed the
present disclosure by supplying the metal chloride raw material at
a flow rate adapted to form the film on both the complex-shaped
portion and the flat portion.
<Example of Film Forming Apparatus>
[0029] FIG. 1 is a sectional view showing an example of a tungsten
film forming apparatus which is used in implementing a metal film
forming method according to the present disclosure.
[0030] A film forming apparatus 100 includes a chamber 1, a
susceptor 2 configured to horizontally support a semiconductor
wafer W (hereinafter, simply referred to as a "wafer") as a target
substrate inside the chamber 1, a shower head 3 configured to
supply a process gas into the chamber 1 in the form of a shower, an
exhaust part 4 configured to exhaust an interior of the chamber 1,
a process gas supply mechanism 5 configured to supply the process
gas into the shower head 3, and a controller 6.
[0031] The chamber 1 is made of a metal such as Al and has a
substantially cylindrical shape. A loading/unloading port 11
through which the wafer W is loaded into and unloaded from the
chamber 1 is formed in a sidewall of the chamber 1. The
loading/unloading port 11 is opened and closed by a gate valve 12.
An annular exhaust duct 13 having a rectangular cross-section is
installed on a main body of the chamber 1. The exhaust duct 13 has
a slit 13a formed along an inner peripheral surface of the exhaust
duct 13. Further, the exhaust duct 13 has an exhaust port 13b
formed in an outer wall of the exhaust duct 13. A ceiling wall 14
is installed on a top face of the exhaust duct 13 so as to block an
upper opening of the chamber 1. A sealing ring 15 is air-tightly
installed between the ceiling wall 14 and the exhaust duct 13.
[0032] The susceptor 2 has a disk shape which corresponds to a size
of the wafer W, and is supported by a support member 23. The
susceptor 2 is made of a ceramic material such as an aluminum
nitride (AlN) or a metallic material such as an aluminum- or
nickel-based alloy. A heater 21 for heating the wafer W is embedded
in the susceptor 2. The heater 21 is configured to generate heat
based on power supplied from a heater power supply (not shown). An
output of the heater 21 is controlled according to a temperature
signal obtained at a thermocouple (not shown) such that the wafer W
is controlled to a predetermined temperature. The thermocouple is
installed near a wafer mounting surface (where the wafer W is
mounted) in an upper surface of the susceptor 2.
[0033] The susceptor 2 is provided with a cover member 22 made of
ceramics such as alumina to cover an outer peripheral area of the
wafer mounting surface and a lateral side of the susceptor 2.
[0034] The support member 23 configured to support the susceptor 2
is configured to extend from the center of a lower surface of the
susceptor 2 toward a position below the chamber 1 through a hole
formed in a bottom wall of the chamber 1. A lower end of the
support member 23 is connected to an elevating mechanism 24. With
an operation of the elevating mechanism 24, the susceptor 2 is
configured to vertically move between a process position (a current
position of the susceptor 2 shown in FIG. 1) and a transfer
position (indicated by a dashed double-dotted line in FIG. 1) where
the wafer W can be transferred, by the support member 23. Further,
a flange part 25 through which the support member 23 penetrates is
installed at a position below the chamber 1. A bellows 26 is
installed between a bottom surface of the chamber 1 and the flange
25. The bellows 26 is configured to isolate an internal atmosphere
of the chamber 1 from ambient air and to be flexible with the
vertical movement of the susceptor 2.
[0035] Three wafer support pins 27 (only two of them are shown in
FIG. 1) are installed to protrude upward from an elevating plate
27a in the vicinity of the bottom surface of the chamber 1. The
wafer support pins 27 are configured to be lifted and lowered by
the elevating plate 27a with an operation of an elevating mechanism
28 installed below the chamber 1. Further, the wafer support pins
27 are configured to penetrate through-holes 2a formed in the
susceptor 2 placed at the transfer position so that they come in
and out of the upper surface of the susceptor 2. By lifting and
lowering the wafer support pins 27 in this way, the wafer W is
transferred between a wafer transfer mechanism (not shown) and the
susceptor 2.
[0036] The shower head 3 made of a metal is installed to face the
susceptor 2, and has a diameter substantially identical to that of
the susceptor 2. The shower head 3 includes a main body 31 fixed to
the ceiling wall 14 of the chamber 1, and a shower plate 32
connected to a lower portion of the main body 31. A gas diffusion
space 33 is defined between the main body 31 and the shower plate
32. The gas diffusion space 33 is connected to a gas inlet hole 36
which is formed to penetrate both central portions of the main body
31 and the ceiling wall 14 of the chamber 1. The shower plate 32A
has an annular protrusion 34 which is formed to protrude downward
from a peripheral portion of the shower plate 32. Gas discharge
holes 35 are formed in an inner flat surface of the shower plate 32
other than the annular protrusion 34.
[0037] When the susceptor 2 is placed at the process position, a
process space 37 is defined between the shower plate 32 and the
susceptor 2, and the annular protrusion 34 and an upper surface of
the cover member 22 of the susceptor 2 approach each other to form
an annular gap 38.
[0038] The exhaust part 4 includes an exhaust pipe 41 connected to
the exhaust port 13b of the exhaust duct 13, and an exhaust
mechanism 42 connected to the exhaust pipe 41. The exhaust
mechanism 42 is provided with a vacuum pump, a pressure control
valve or the like. When the wafer is processed, a gas inside the
chamber 1 flows to the exhaust duct 13 through the slit 13a, and
subsequently, is exhausted from the exhaust duct 13 through the
exhaust pipe 41 by the exhaust mechanism 42 of the exhaust part
4.
[0039] The process gas supply mechanism 5 includes a WCl.sub.6 gas
supply mechanism 51 for supplying a WCl.sub.6 gas used as a
tungsten chloride gas that is a tungsten raw material gas, a first
H.sub.2 gas supply source 52 for supplying an H.sub.2 gas as a main
reduction gas, a second H.sub.2 gas supply source 53 for supplying
an H.sub.2 gas as an additive reduction gas, and a first N.sub.2
gas supply source 54 and a second N.sub.2 gas supply source 55 for
supplying an N.sub.2 gas as a purge gas. Further, the process gas
supply mechanism 5 includes a WCl.sub.6 gas supply line 61
installed to extend from the WCl.sub.6 gas supply source 51, a
first H.sub.2 gas supply line 62 installed to extend from the first
H.sub.2 gas supply source 52, a second H.sub.2 gas supply line 63
installed to extend from the second H.sub.2 gas supply source 53, a
first N.sub.2 gas supply line 64 which is installed to extend from
the first N.sub.2 gas supply source 54 and through which the
N.sub.2 gas is supplied to the WCl.sub.6 gas supply line 61, and a
second N.sub.2 gas supply line 65 which is installed to extend from
the second N.sub.2 gas supply source 55 and through which the
N.sub.2 gas is supplied to the first H.sub.2 gas supply line
62.
[0040] The first N.sub.2 gas supply line 64 is branched into a
first continuous N.sub.2 gas supply line 66 through which the
N.sub.2 gas is always supplied during the ALD method-based film
forming process, and a first flash purge line 67 through which the
N.sub.2 gas is supplied only during a purge process. Similarly, the
second N.sub.2 gas supply line 65 is branched into a second
continuous N.sub.2 gas supply line 68 through which the N.sub.2 gas
is always supplied during the ALD method-based film forming
process, and a second flash purge line 69 through which the N.sub.2
gas is supplied only during the purge process. The first continuous
N.sub.2 gas supply line 66 and the first flash purge line 67 are
connected to a first connection line 70 which is connected to the
WCl.sub.6 gas supply line 61. Further, the second H.sub.2 gas
supply line 63, the second continuous N.sub.2 gas supply line 68
and the second flash purge line 69 are connected to a second
connection line 71 which is connected to the first H.sub.2 gas
supply line 62. The WCl.sub.6 gas supply line 61 and the first
H.sub.2 gas supply line 62 are joined in a joint pipe 72. The joint
pipe 72 is connected to the aforementioned gas inlet hole 36.
[0041] At most downstream sides of the WCl.sub.6 gas supply line
61, the first H.sub.2 gas supply line 62, the second H.sub.2 gas
supply line 63, the first continuous N.sub.2 gas supply line 66,
the first flash purge line 67, the second continuous N.sub.2 gas
supply line 68 and the second flash purge line 69, on-off valves
73, 74, 75, 76, 77, 78 and 79 for switching the supply of
respective gases during the ALD process are respectively installed.
Further, mass flow controllers (MFC) 82, 83, 84, 85, 86 and 87 as
flow rate controllers are installed at upstream sides of the on-off
valves 74, 75, 76, 77, 78 and 79 of the first H.sub.2 gas supply
line 62, the second H.sub.2 gas supply line 63, the first
continuous N.sub.2 gas supply line 66, the first flash purge line
67, the second continuous N.sub.2 gas supply line 68 and the second
flash purge line 69, respectively. Furthermore, buffer tanks 80 and
81 are respectively installed in the WCl.sub.6 gas supply line 61
and the first H.sub.2 gas supply line 62 such that required gases
can be supplied in a short period of time.
[0042] The WCl.sub.6 gas supply mechanism 51 includes a
film-forming raw material tank 91 which stores WCl.sub.6 therein.
WCl.sub.6 is solid at room temperature. Such a solid WCl.sub.6 is
stored in the film-forming raw material tank 91. A heater 91a is
installed around the film-forming raw material tank 91 so that the
film-forming raw material within the film-forming raw material tank
91 is heated to a suitable temperature, thus sublimating the
WCl.sub.6 material The WCl.sub.6 gas supply line 61 is inserted
into the film-forming raw material tank 91 from above.
[0043] Further, the WCl.sub.6 gas supply mechanism 51 includes: a
carrier gas pipe 92 inserted into the film-forming raw material
tank 91 from above; a carrier N.sub.2 gas supply source 93 for
supplying an N.sub.2 gas as a carrier gas to the carrier gas pipe
92; a mass flow controller (MFC) 94 as a flow rate controller and
on-off valves 95a and 95b positioned at a downstream side of the
mass flow controller 94, which are connected to the carrier gas
pipe 92; and on-off valves 96a and 96b and a flowmeter (MFM) 97,
which are installed in the WCl.sub.6 gas supply line 61 in the
vicinity of the film-forming raw material tank 91. In the carrier
gas pipe 92, the on-off valve 95a is installed directly below the
mass flow controller 94, whereas the on-off valve 95b is installed
at a side where the carrier gas pipe 92 is inserted into the
film-forming raw material tank 91. The on-off valves 96a and 96b
and the flowmeter 97 are sequentially arranged in the WCl.sub.6 gas
supply line 61 starting from a side where the WCl.sub.6 gas supply
line 61 is inserted into the film-forming raw material tank 91.
[0044] A bypass pipe 98 is installed to connect a portion between
the on-off valve 95a and the on-off valve 95b in the carrier gas
pipe 92 to a portion between the on-off valve 96a and the on-off
valve 96b in the WCl.sub.6 gas supply line 61. The bypass pipe 98
includes an on-off valve 99 installed therein. By closing the
on-off valves 95b and 96a and opening the on-off valves 99, 95a and
96b, the N.sub.2 gas supplied from the carrier N.sub.2 gas supply
source 93 is introduced to the WCl.sub.6 gas supply line 61 through
a series of the carrier gas pipe 92 and the bypass pipe 98 so that
the WCl.sub.6 gas supply line 61 can be purged.
[0045] One end of an EVAC pipe 101 is connected to a downstream
position of the flowmeter 97 in the WCl.sub.6 gas supply line 61
and the other end thereof is connected to the exhaust pipe 41.
On-off valves 102 and 103 are installed in the vicinity of the
WCl.sub.6 gas supply line 61 and the exhaust pipe 41 in the EVAC
pipe 101, respectively. Further, an on-off valve 104 is installed
at a downstream side of a connection position where the EVAC pipe
101 is connected to the WCl.sub.6 gas supply line 61. The on-off
valves 104, 99, 95a and 95b are closed and the on-off valves 102,
103, 96a and 96b are opened to vacuum-exhaust the interior of the
film-forming raw material tank 91 by the exhaust mechanism 42.
[0046] The controller 6 includes: a process controller equipped
with a microprocessor (computer) for controlling respective
components of the film forming apparatus 100, i.e., the valves, the
power supplies, the heaters, the pumps and the like; a user
interface; and a storage part. The respective components of the
film forming apparatus 100 are configured to be electrically
connected to the process controller such that they are controlled
by the process controller. The user interface is connected to the
process controller, and includes a keyboard that enables an
operator to input commands for managing the respective components
of the film forming apparatus 100, a display that visually displays
operational states of the respective components of the film forming
apparatus 100, and the like. The storage part is also connected to
the process controller and stores a control program for
implementing various processes which are performed in the film
forming apparatus 100 under the control of the process controller;
a control program (i.e., a process recipe) for executing
predetermined processes in the respective components of the film
forming apparatus 100 depending on process conditions; various
databases; or the like. The processing recipe is stored in a
storage medium (not shown) of the storage part. The storage medium
may be a fixedly-installed medium such as a hard disk, or a
portable medium such as a CDROM, a DVD and a semiconductor memory.
Further, the process recipe may be appropriately transmitted from
another device through, e.g., a dedicated line. If necessary, a
predetermined process recipe may be called from the storage part
according to an instruction from the user interface and then
executed by the process controller so that a desired process is
performed in the film forming apparatus 100 under the control of
the process controller.
<Film Forming Method>
[0047] Next, an embodiment of a tungsten film forming method which
is performed using the film forming apparatus 100 configured as
above will be described.
(Summary of Film Forming Method)
[0048] First, a summary of the film forming method will be
described.
[0049] The film forming method according to this embodiment is
applied to a case where a tungsten film is formed on a wafer having
a flat portion and a complex-shaped portion. The complex-shaped
portion refers to a portion in which a recess having a relatively
high aspect ratio is formed, whereas the flat portion refers to a
portion in which no recess is formed or a recess having a
relatively low aspect ratio is formed.
[0050] FIGS. 2A and 2B are cross-sectional process views
schematically showing processes of the tungsten film forming method
according to this embodiment.
[0051] First, as shown in FIG. 2A, a wafer W is prepared in which
an insulation film 202 such as an SiO.sub.2 film is formed on an Si
substrate 201 and then a base film 203 is formed on the insulation
film 202. Although in FIG. 2A, the wafer W has been shown in a
planar shape for the sake of simplicity, the wafer W has the
complex-shaped portion and the flat portion in practice.
[0052] An example of the base film 203 may include a titanium-based
material film such as a TiN film, a TiSiN film, a Ti silicide film,
a Ti film, a TiON film, a TiAlN film or the like. In some
embodiments, an example of the base film 203 may include a
tungsten-based compound film such as a WN film, a WSi.sub.x film, a
WSiN film or the like. The formation of the base film 203 on the
insulation film 202 allows the tungsten film to be formed with good
adhesion.
[0053] Subsequently, the ALD method of sequentially supplying the
WCl.sub.6 gas as the tungsten chloride gas and the H.sub.2 gas as
the reduction gas into the chamber 1, while purging the interior of
the chamber 1, is performed during the course of sequentially
supplying the WCl.sub.6 gas and the H.sub.2 gas. Thus, a tungsten
film 204 is formed on the base film 203. In this embodiment, as
shown in FIG. 2B, a process of supplying the WCl.sub.6 gas at a
relatively low flow rate to form a first tungsten film (1st W film)
205 and a process of supplying the WCl.sub.6 gas at a relatively
high flow rate to form a second tungsten film (2nd W film) 206 are
alternately repeated. Thus, the first tungsten film 205 and the
second tungsten film 206 are alternately formed in multiple layers
so that the tungsten film 204 is obtained.
[0054] Next, the reason for employing such a film forming method
will be described.
[0055] When the tungsten film is formed by the ALD method using the
WCl.sub.6 gas as the tungsten chloride gas and the H.sub.2 gas as
the reduction gas, an adsorption operation of the WCl.sub.6 gas and
a reduction operation of WCl.sub.6 by the H.sub.2 gas as the
reduction gas are repeated as shown in FIG. 3. A reaction that
generates tungsten by reducing the adsorbed WCl.sub.6 produces HCl
according to the following Formula (1):
WCl.sub.6(ad)+3H.sub.2.fwdarw.(g).fwdarw.-W(s)+6HCl (1)
[0056] Since HCl produced by this reaction has a strong etching
property, it etches the tungsten film formed by a reaction
according to the following Formula (2):
W(s)+5WCl.sub.6(g).fwdarw.6WCl.sub.x (2)
[0057] Such a reaction impedes the formation of the tungsten film.
As shown in FIG. 4A, since a flow rate of the WCl.sub.6 gas
supplied per unit area in the flat portion is high (i.e., since a
partial pressure of the WCl.sub.6 gas is high), an amount of HCl
per unit area becomes larger so that etching is likely to progress,
which lowers a film forming rate of the tungsten film. On the
contrary, as shown in FIG. 4B, since a patterned portion has an
increased surface area so that the flow rate of the WCl.sub.6 gas
supplied per unit area in the patterned portion is low (i.e., the
partial pressure of the WCl.sub.6 gas is low), the amount of HCl
per unit area becomes smaller so that etching is suppressed, which
makes it possible to maintain the film forming rate of the tungsten
film at a high level.
[0058] In particular, when the tungsten film is formed on a
semiconductor device such as 3D NAND flash memory having a memory
cell as the complex-shaped portion and the flat portion, the
WCl.sub.6 gas used as the film-forming raw material is required to
be supplied at a relatively high flow rate in order to form a film
on the entire region of the complex-shaped portion. However, if the
WCl.sub.6 gas is supplied at a sufficient flow rate to form the
film on the entire region of the complex-shaped portion, the
tungsten film is hardly deposited on the flat portion due to the
HCL-based etching action.
[0059] Such a problem will be described with an example of a
manufacturing process of the 3D NAND flash memory with reference to
FIGS. 5 and 6. In the manufacturing process of the 3D NAND flash
memory, a base structure (not shown) is first formed on a Si
substrate (not shown), and subsequently, a stack body 303 that is
obtained by alternately stacking SiO.sub.2 films 301 and SiN films
302 in a level of, e.g., 24 to 70 layers, is formed on the base
structure. Thereafter, an SiO.sub.2 film 304 having a relatively
thick thickness is formed on the stack body 303. Subsequently, a
trench 305 and holes 306 are vertically formed by a dry etching,
thereby obtaining a structure shown in FIG. 5A.
[0060] Thereafter, a columnar body 307 composed of an IPD film, a
charge trap layer, a tunnel oxide film, a channel poly and a
central oxide film is formed in each of the holes 306.
Subsequently, the SiN film 302 is removed by a wet etching to form
spaces 308, thereby obtaining a structure shown in FIG. 5B.
[0061] Thereafter, as shown in FIG. 5C, the base film 203 composed
of a TiN film is formed over the entire surface of the structure
shown in FIG. 5B. Subsequently, as shown in FIG. 6A, the tungsten
film 204 is formed on the base film 203 composed of the TiN film.
Thereafter, as shown in FIG. 6B, an extra region of the tungsten
film 204 is removed by the wet etching.
[0062] In this way, a memory cell having a stack structure of the
SiO.sub.2 films 301 and the tungsten film 204 is formed. A portion
of the stack structure corresponds to the complex-shaped portion
having a high aspect ratio in which the number of stacked layers is
large and sizes of the spaces 308 are miniaturized. Therefore, in
order to widely diffuse the WCl.sub.6 gas up to the lower space 308
and to form the tungsten film with a high step coverage, the flow
rate of the WCl.sub.6 gas needs to be increased up to a certain
level.
[0063] However, since a surface of the SiO.sub.2 film 304 formed at
the uppermost position corresponds to the flat portion, if the
WCl.sub.6 gas is supplied at a sufficient flow rate to cover the
entire region of the complex-shaped portion, the HCL-based etching
action is likely to progress in the flat portion. As such, hardly
any tungsten film is deposited. This situation will be described
with reference to FIG. 7. FIG. 7 is a graph in which a horizontal
axis indicates a cycle rate (a deposition amount per cycle) during
the ALD process and a vertical axis indicates a step coverage. It
can be seen from FIG. 7 that if the WCl.sub.6 gas is supplied at a
sufficient flow rate to ensure a high step coverage in the
complex-shaped portion, hardly any tungsten film is formed on the
flat portion.
[0064] Meanwhile, if the flow rate of the WCl.sub.6 gas becomes
higher, the HCL-based etching action is weak so that the tungsten
film may be formed even in the flat portion. However, even if the
WCl.sub.6 gas is supplied with a level at which the tungsten film
can be formed in the flat portion, it is difficult to widely spread
the WCl.sub.6 gas over the entire region of the complex-shaped
portion.
[0065] In view of the foregoing, the process of supplying the
WCl.sub.6 gas at a relatively low flow rate to form the first
tungsten film 205 and the process of supplying the WCl.sub.6 gas at
a relatively high flow rate to form the second tungsten film 206
are alternately repeated. Thus, it is possible to deposit the
tungsten film on both the complex-shaped portion and the flat
portion.
[0066] The tungsten film 204 is required to be formed with good
buriability (high step coverage). To this end, the tungsten film
204 is formed by the ALD method which sequentially supplies the
WCl.sub.6 gas as the tungsten chloride gas and the H.sub.2 gas as
the reduction gas into the chamber 1 while purging the interior of
the chamber 1 in the course of sequentially supplying the WCl.sub.6
gas and the H.sub.2 gas. Further, this embodiment is not limited to
the ALD method in a strict sense, and tungsten film may be formed
according to a sequence equivalent to the ALD method.
[0067] The flow rate of the WCl.sub.6 gas in the course of forming
the first tungsten film 205 may be determined as a sufficient level
to form the tungsten film in the flat portion by minimizing the
influence of the HCL-based etching action. Since an appropriate
range of the flow rate of the WCl.sub.6 gas varies depending on,
e.g., a size of the chamber 1, the partial pressure of the
WCl.sub.6 gas inside the chamber 1 may be used as an indicator of
the flow rate of WCl.sub.6 gas. From the viewpoint of effectively
forming the tungsten film in the flat portion, the partial pressure
of the WCl.sub.6 gas may be 1 Torr (133.3 Pa) or less. In some
embodiments, the partial pressure of the WCl.sub.6 gas may be 0.1
Torr (13.33 Pa) or less.
[0068] In some embodiments, the flow rate of the WCl.sub.6 gas in
the course of forming the second tungsten film 206 may be
determined as a sufficient level to form the tungsten film over the
entire region of the complex-shaped portion that is a portion where
a device is to be formed. The partial pressure of the WCl.sub.6 gas
inside the chamber 1 may fall within a range of approximately 0.5
to 10 Torr (66.7 to 1,333 Pa).
[0069] In the formation of the tungsten film 204, either of the
first tungsten film 205 and the second tungsten film 206 may be
first deposited, but the first tungsten film 205 having the
relatively low flow rate of the WCl.sub.6 gas may be first
deposited. The reason for this is that, in a region where the
tungsten film in an initial stage of the film forming process is
hardly deposited or a deposition amount thereof is small, the
WCl.sub.6 gas is directly supplied to the base film 203 so that the
base film 203 is etched by the WCl.sub.6 gas.
[0070] In other words, the reason for the above is that, when the
base film 203 is a TiN film, an etching reaction as expressed by
the following Formula (3) is induced between TiN and WCl.sub.6
gases and a film thickness of the base film 203 is decreased by the
etching reaction as the flow rate of the WCl.sub.6 gas
increases.
TiN(s)+WCl.sub.6(g).fwdarw.TiCl.sub.4(g)+WCl.sub.x(g) (3)
[0071] Similarly, even when other titanium-based material films and
tungsten compound films are used as the base film 203, the base
film 203 is etched by the WCl.sub.6 gas as the tungsten chloride
gas. Thus, the first tungsten film 205 may be formed
preferentially.
[0072] In some embodiments, as shown in FIG. 8, from the viewpoint
of preventing the etching of the base film 203, an initial tungsten
film 207 may be additionally formed on the base film 203 before
forming the tungsten film 204. By additionally forming the initial
tungsten film 207 as described above, the initial tungsten film 207
can be configured to have a thickness suitable to effectively
prevent the base film 203 from being etched depending on the flow
rate of the WCl.sub.6 gas supplied to form the second tungsten film
206. The initial tungsten film 207 can be formed by the ALD method.
However, since the initial tungsten film 207 is formed to prevent
the base film 203 from being etched by the WCl.sub.6 gas and does
not require buriability similar to that of the tungsten film 204,
the initial tungsten film 207 may be formed by the CVD method by
simultaneously supplying the WCl.sub.6 gas and the H.sub.2 gas into
the chamber 1. Further, a partial pressure of the WCl.sub.6 gas
during the formation of the initial tungsten film 207 is 1 Torr
(133.3 Pa) or less as in the first tungsten film 205, in some
embodiments, 0.1 Torr (13.33 Pa) or less. At this time, the partial
pressure of the WCl.sub.6 gas may be different from that during the
formation of the first tungsten film 205.
[0073] Further, when the tungsten film 204 is subjected to the wet
etching, for example, when the extra region of the formed tungsten
film 204 is subjected to the wet etching in the manufacturing
process of the 3D NAND flash memory as shown in FIGS. 6A and 6B, if
a finally-formed film in the formed tungsten film 204 is the second
tungsten film for which the flow rate of the WCl.sub.6 gas is low,
the HCL-based etching action becomes strong. Thus, a surface of the
tungsten film 204 becomes smooth so that a slight gap 208 is formed
at a central portion of the tungsten film 204 as shown in FIG. 9A.
If the wet etching is performed in such a state, some of the
tungsten film in the buried portion is also etched as shown in FIG.
9B. For such a reason, it is preferable that the finally-formed
film in the tungsten film 204 is the first tungsten film 205 which
is formed by supplying the WCl.sub.6 gas at a relatively low flow
rate and manifests a weak etching action. That is to say, since the
first tungsten film 205 is finally formed, the etching action is
weak, whereby the gap 208 can be buried as shown in FIG. 9C.
[0074] In some embodiments, as shown in FIG. 10, a top coating
tungsten film 209 may be additionally formed on the surface of the
tungsten film 204 to bury the gap 208 defined in the tungsten film
204. By additionally forming the top coating tungsten film 209 as
described above, the gap 208 can be appropriately buried by
properly adjusting the flow rate of the WCl.sub.6 gas and a
thickness of the top coating tungsten film 209. The top coating
tungsten film 209 may be formed by the ALD method. However, since
the top coating tungsten film 209 is formed to bury the gap 208 and
does not require buriability similar to that of the tungsten film
204, the top coating tungsten film 209 may be formed by the CVD
method by simultaneously supplying the WCl.sub.6 gas and the
H.sub.2 gas into the chamber 1. Further, it is preferable that the
partial pressure of the WCl.sub.6 gas in the course of forming the
top coating tungsten film 209 is 1 Torr (133.3 Pa) or less as in
the first tungsten film 205, in some embodiments, 0.1 Torr (13.33
Pa) or less. At this time, the partial pressure of the WCl.sub.6
gas in the course of forming the top coating tungsten film 209 may
be different from that in the course of forming the initial
tungsten film 205.
[0075] Although the first tungsten film 205 and the second tungsten
film 206 may be sequentially stacked one above another, such a
sequential stack structure may be alternately repeated two times or
more, in some embodiments, five times or more. Further, as
described above, from the viewpoint of preventing the base film
from being etched and preventing the buried tungsten from being
etched during the wet etching of the tungsten film, the first
tungsten films 205 may be formed at initial and final film-forming
stages. In this case, a minimum unit of the stack structure is a
three-layered structure of the first tungsten film 205-the second
tungsten film 206-the first tungsten film 205. However, in the case
where the initial tungsten film 207 or the top coating tungsten
film 209 is formed, a stack sequence in the stack structure is not
particularly restricted as long as at least one layer of the first
tungsten film 205 and at least one layer of the second tungsten
film 206 are formed in the stack structure. In some embodiments,
each of the first tungsten film 205 and the second tungsten film
206 may have a film thickness ranging from 1 to 10 nm.
[0076] Further, although WCl.sub.6 has been described to be used as
the tungsten chloride used in forming the tungsten film 204,
WCl.sub.5 or WCl.sub.4 may be used instead of WCl.sub.6. These
WCl.sub.5 or WCl.sub.4 manifest behaviors substantially equal to
that of WCl.sub.6.
[0077] Further, the reduction gas is not limited to the H.sub.2 gas
but may be other reduction gases which contain hydrogen. Instead of
the H.sub.2 gas, an SiH.sub.4 gas, a B.sub.2H.sub.6 gas, an
NH.sub.3 gas or the like may be used as the reduction gas.
Alternatively, two or more of the H.sub.2 gas, the SiH.sub.4 gas,
the B.sub.2H.sub.6 gas and the NH.sub.3 gas may be supplied.
Moreover, in addition to these gases, other reduction gases such as
a PH.sub.3 gas or an SiH.sub.2Cl.sub.6 gas may be used. From the
viewpoint of further decreasing impurities in the film to obtain a
low resistance value, the H.sub.2 gas may be used.
[0078] An inert gas such as an N.sub.2 gas or an Ar gas may be used
as the purge gas or the carrier gas.
[0079] In some embodiments, a temperature of the wafer during the
formation of the tungsten film 204 may be 300 degrees C. or more.
Further, an internal pressure of the chamber 1 may range from 20 to
100 Torr (from 2,666 to 13,330 Pa).
<Specific Sequence Using Film Forming Apparatus of FIG.
1>
[0080] Next, a specific sequence when using the film forming
apparatus of FIG. 1 will be described.
[0081] First, the wafer W having a predetermined structure is
loaded into the chamber 1 through the loading/unloading port 11 and
subsequently, mounted on the susceptor 2 which has been heated to a
predetermined temperature by the heater 21. The susceptor 2 is
lifted up to the process position. The interior of the chamber 1 is
vacuum-exhausted to a predetermined degree of vacuum. The on-off
valves 104, 95a, 95b and 99 are closed and the on-off valves 102,
103, 96a and 96b are opened so that the interior of the
film-forming raw material tank 91 is vacuum-exhausted through the
EVAC pipe 101. Thereafter, the on-off valves 76 and 78 are opened
and the on-off valves 73, 74, 75, 77 and 79 are closed such that
the N.sub.2 gases supplied from the first N.sub.2 gas supply source
54 and the second N.sub.2 gas supply source 55 are respectively
introduced into the chamber 1 through the first continuous N.sub.2
gas supply line 66 and the second continuous N.sub.2 gas supply
line 68, thereby increasing the internal pressure of the chamber 1
and stabilizing the temperature of the wafer W mounted on the
susceptor 2.
[0082] After the internal pressure of the chamber 1 reaches a
predetermined pressure, the on-off valves 102 and 103 are closed
and the on-off valves 104, 95a and 95b are opened such that the
internal pressure of the film-forming raw material tank 91 is
increased, thus establishing a condition in which the WCl.sub.6 gas
as the tungsten raw material can be supplied.
[0083] In this state, the WCl.sub.6 gas as the film-forming raw
material gas, the H.sub.2 gas as the reduction gas, and the N.sub.2
gas as the purge gas are supplied in a sequential manner as
described below. As described above, by changing the flow rate
(partial pressure) of the WCl.sub.6 gas to be supplied, the first
tungsten film 205 and the second tungsten film 206 are alternately
formed to obtain the tungsten film 204.
[0084] FIG. 11 is a view showing an example of a gas supply
sequence when forming the first tungsten film 205 and the second
tungsten film 206.
[0085] First, the on-off valves 76 and 78 are opened and the
N.sub.2 gases are continuously supplied from the first N.sub.2 gas
supply source 54 and the second N.sub.2 gas supply source 55
through the first continuous N.sub.2 gas supply line 66 and the
second continuous N.sub.2 gas supply line 68. Further, the on-off
valves 73 and 75 are opened and the WCl.sub.6 gas is supplied from
the WCl.sub.6 gas supply mechanism 51 through the WCl.sub.6 gas
supply line 61 into the process space 37 in the chamber 1. The
H.sub.2 gas (i.e., the additive H.sub.2 gas) as the additive
reduction gas is supplied into the chamber 1 through the second
H.sub.2 gas supply line 63 extending from the second H.sub.2 gas
supply source 53 (in Step S1). At this time, the WCl.sub.6 gas is
first stored in the buffer tank 80 and then supplied into the
chamber 1.
[0086] In Step S1, WCl.sub.6 is adsorbed onto a surface of the
wafer W. At this time, WCl.sub.6 is activated by the H.sub.2 gas
which is simultaneously supplied into the chamber 1.
[0087] Subsequently, while the N.sub.2 gas is continuously supplied
through the first continuous N.sub.2 gas supply line 66 and the
second continuous N.sub.2 gas supply line 68, the on-off valves 73
and 75 are closed to stop the supply of the WCl.sub.6 gas and the
H.sub.2 gas, and simultaneously, the on-off valves 77 and 79 are
opened to supply the N.sub.2 gas (i.e., a flash purge N.sub.2 gas)
through the first flash purge line 67 and the second flash purge
line 69. Thus, a high flow rate of the N.sub.2 gas purges an extra
WCl.sub.6 gas and the like existing in the process space 37 (in
Step S2).
[0088] Subsequently, the on-off valves 77 and 79 are closed to stop
the supply of the N.sub.2 gas through the first flash purge line 67
and the second flash purge line 69, while the N.sub.2 gas is
continuously supplied through the first continuous N.sub.2 gas
supply line 66 and the second continuous N.sub.2 gas supply line
68. At this state, the on-off valve 74 is opened to supply the
H.sub.2 gas (i.e., the main H.sub.2 gas) as the main reduction gas
from the first H.sub.2 gas supply source 52 into the process space
37 through the first H.sub.2 gas supply line 62 (in Step S3). At
this time, the H.sub.2 gas is first stored in the buffer tank 81
and then supplied into the chamber 1.
[0089] In Step S3, WCl.sub.6 adsorbed onto the wafer W is reduced.
At this time, a flow rate of the main H.sub.2 gas corresponds to a
sufficient level to induce the reduction reaction and is lower than
that of the additive H.sub.2 gas in Step S1.
[0090] Subsequently, while the N.sub.2 gas is continuously supplied
through the first continuous N.sub.2 gas supply line 66 and the
second continuous N.sub.2 gas supply line 68, the on-off valve 74
is closed to stop the supply of the H.sub.2 gas through the first
H.sub.2 gas supply line 62, and the on-off valves 77 and 79 are
opened to stop the supply of the N.sub.2 gas (i.e., the flash purge
N.sub.2 gas) through the first flash purge line 67 and the second
flash purge line 69. Thus, like in Step S2, a high flow rate of the
N.sub.2 gas purges the extra H.sub.2 gas existing in the process
space 37 (in Step S4).
[0091] A single cycle including Steps S1 to S4 described above is
performed in a short period of time to form a unit tungsten film
having a thin thickness. Further, the single cycle including Steps
1 to 4 is repeated a multiple number of times to form the first
tungsten film and the second tungsten film each having a desired
film thickness. The film thicknesses of the first tungsten film and
the second tungsten film at this time can be controlled according
to the number of repetitions of the single cycle.
[0092] In Step S1, in parallel with the supply of the WCl.sub.6
gas, the additive reduction gas is also supplied through the second
H.sub.2 gas supply line 63 to activate the WCl.sub.6 gas. This
facilitates a film formation reaction in the subsequent Step S3. It
is therefore possible to keep the step coverage at a high level and
increase a thickness of the film formed per cycle, thus increasing
a film forming rate. The flow rate of the H.sub.2 gas at this time
needs to be controlled to suppress the CVD-based reaction while
ensuring the ALD-based reaction. Thus, the flow rate of the H.sub.2
gas may range from 100 to 500 sccm (mL/min) In some embodiments, as
shown in FIG. 12, the additive H.sub.2 gas may be always supplied
through the second H.sub.2 gas supply line 63 during the period of
Steps S2 to S4. With this configuration, when the WCl.sub.6 gas is
supplied, the additive H.sub.2 gas as the additive reduction gas is
also supplied, thus activating the WCl.sub.6 gas. The flow rate of
the H.sub.2 gas at this time may range from 10 to 500 sccm (mL/min)
from the viewpoint of suppressing the CVD-based reaction and
keeping the ALD-based reaction. However, if a good film formation
reaction is induced even in the absence of the additive H.sub.2
gas, the additive H.sub.2 gas may be omitted.
[0093] In the above sequence, the N.sub.2 gas as the purge gas
always flows from the first continuous N.sub.2 gas supply line 66
and the second continuous N.sub.2 gas supply line 68 to the
WCl.sub.6 gas supply line 61 and the first H.sub.2 gas supply line
62 during the period of Steps S1 to S4, while the WCl.sub.6 gas and
the H.sub.2 gas are intermittently supplied in Steps S1 and S3. It
is therefore possible to improve a replacement efficiency of gas
inside the process space 37. Further, the N.sub.2 gas is supplied
through each of the first flash purge line 67 and the second flash
purge line 69 to purge the process space 37 in Steps S2 and S4.
This further improves the replacement efficiency of gas inside the
process space 37. It is therefore possible to control the thickness
of the unit tungsten film at a good level.
[0094] In the film forming apparatus 100 shown in FIG. 1, the
buffer tanks 80 and 81 are installed in the WCl.sub.6 gas supply
line 61 and the first H.sub.2 gas supply line 62, respectively.
This facilitates the supply of the WCl.sub.6 gas and the H.sub.2
gas in a short period of time. Thus, even if a period of the single
cycle is short, it is possible to easily supply the WCl.sub.6 gas
and the H.sub.2 gas at a flow rate required for Steps S1 and
S3.
<Film Formation Conditions>
[0095] Next, an example of film formation conditions of the first
tungsten film 205 and the second tungsten film 206 will be
described.
(1) For the first tungsten film 205
[0096] i) ALD
[0097] Pressure: 20 to 100 Torr (2,666 to 13,330 Pa)
[0098] Temperature: 300 degrees C. or more (in some embodiments,
450 to 600 degrees C.)
[0099] Flow Rate of WCl.sub.6 Gas: 0.1 to 10 sccm (mL/min) [0100]
(Flow Rate of Carrier Gas: 1 to 1,000 sccm (mL/min))
[0101] Partial Pressure of WCl.sub.6 Gas (previously described): 1
Torr (133.3 Pa) or less (in some embodiments, 0.1 Torr (13.33 Pa)
or less)
[0102] Flow Rate of Main H.sub.2 Gas: 10 to 5,000 sccm (mL/min)
[0103] Flow Rate of Continuously-Supplied N.sub.2 Gas: 10 to 10,000
sccm (mL/min) [0104] (through the first and second Continuous
N.sub.2 Gas supply lines 66 and 68)
[0105] Flow Rate of Flash Purge N.sub.2 Gas: 100 to 100,000 sccm
(mL/min) [0106] (through the first and second Flash Purge Lines 67
and 69)
[0107] Period of Time of Step S1 (Per Cycle): 0.01 to 5 sec
[0108] Period of Time of Step S3 (Per Cycle): 0.1 to 5 sec
[0109] Period of Time of each of Steps S2 and S4 (Purging) (Per
Cycle): 0.1 to 5 sec
[0110] Period of Supply Time of Additive H.sub.2 Gas in Step S1
(Per Cycle): 0.01 to 0.3 sec
[0111] Heated Temperature of Film-forming raw material tank: 130 to
190 degrees C.
[0112] ii) CVD
[0113] Pressure: 20 to 100 Torr (2,666 to 13,330 Pa)
[0114] Temperature: 300 degrees C. or more (in some embodiments,
450 to 600 degrees C.)
[0115] Flow Rate of WCl.sub.6 Gas: 0.1 to 10 sccm (mL/min) [0116]
(Flow Rate of Carrier Gas: 1 to 1,000 sccm (mL/min))
[0117] Partial Pressure of WCl.sub.6 Gas (previously described): 1
Torr (133.3 Pa) or less (in some embodiments, 0.1 Torr (13.33 Pa)
or less)
[0118] Flow Rate of Main H.sub.2 Gas: 10 to 5,000 sccm (mL/min)
[0119] Flow Rate of N.sub.2 Gas: 10 to 10,000 sccm (mL/min)
(2) For the second tungsten film 206
[0120] Pressure: 5 to 50 Torr (666.5 to 6,665 Pa)
[0121] Temperature: 300 degrees C. or more (in some embodiments,
450 to 600 degrees C.)
[0122] Flow Rate of WCl.sub.6 Gas: 3 to 60 sccm (mL/min) [0123]
(Flow Rate of Carrier Gas: 100 to 2,000 sccm (mL/min))
[0124] Partial Pressure of WCl.sub.6 Gas: 0.5 to 10 Torr (66.7 to
1,333 Pa)
[0125] Flow Rate of Main H.sub.2 Gas: 2,000 to 8,000 sccm
(mL/min)
[0126] Flow Rate of Additive H.sub.2 Gas (previously described):
100 to 500 sccm (mL/min)
[0127] Flow Rate of Continuously-Supplied N.sub.2 Gas: 100 to 500
sccm (mL/min) [0128] (through the first and second Continuous
N.sub.2 Gas supply lines 66 and 68)
[0129] Flow Rate of Flash Purge N.sub.2 Gas: 500 to 3,000 sccm
(mL/min) [0130] (through the first and second Flash Purge Lines 67
and 69)
[0131] Period of Time of Step S1 (Per Cycle): 0.01 to 5 sec
[0132] Period of Time of Step S3 (Per Cycle): 0.1 to 5 sec
[0133] Period of Time of each of Steps S2 and S4 (Purging) (Per
Cycle): 0.1 to 5 sec
[0134] Period of Supply Time of Additive H.sub.2 Gas in Step S1
(Per Cycle): 0.01 to 0.3 sec
[0135] Heated Temperature of Film-Forming Raw Material Tank: 130 to
170 degrees C.
[0136] In some embodiments, the additional formation of the initial
tungsten film 207 and the top coating tungsten film 209 may be
performed under the same conditions as the first tungsten film 205
according to the sequences shown in FIGS. 11 and 12. Further, as
described above, the initial tungsten film 207 and the top coating
tungsten film 209 can be formed by the CVD method. In this case,
the WCl.sub.6 gas and the H.sub.2 gas are simultaneously supplied
from the WCl.sub.6 gas supply line 61 and the first H.sub.2 gas
supply line 62, respectively.
[0137] According to the present disclosure in some embodiments, a
process of supplying a metal chloride raw material at a relatively
low flow rate to form a first tungsten film and a process of
supplying the metal chloride raw material at a relatively high flow
rate to form a second tungsten film are performed. Thus, it is
possible to form a film on both a flat portion and the entire
region of a complex-shaped portion by the processes of forming the
first metal film and the second metal film. Accordingly, when a
metal film is formed on a target substrate having the
complex-shaped portion and the flat portion using the chloride raw
material, the metal film can be formed over the entire region of
the target substrate.
OTHER APPLICATIONS
[0138] While the present disclosure has described exemplary
embodiments, the present disclosure is not limited thereto, but may
be modified in a variety of forms. As an example, although in the
above embodiments, the tungsten film has been described to be
formed using the tungsten chloride as the metal chloride, the
present disclosure can be applied to other cases where a metal
chloride gas and a reduction gas are sequentially supplied to form
a metal film. For example, the present disclosure can be applied to
a case where a molybdenum film is formed by a molybdenum chloride
gas and a reduction gas, or a case where a tantalum film is formed
by a tantalum chloride gas and a reduction gas.
[0139] Further, although in the above embodiments, the
semiconductor wafer has been described to be used as a target
substrate, the semiconductor wafer may be a silicon substrate, or a
compound semiconductor such as GaAs, SiC and GaN or the like. The
present disclosure is not limited to the semiconductor wafer but
may be also applied to a glass substrate used in a flat panel
display (FPD) such as a liquid crystal display, a ceramic substrate
or the like.
[0140] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the disclosure. Indeed, the
embodiments described herein may be embodied in a variety of other
forms. Furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the disclosure. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
disclosure.
* * * * *